The invention is directed to heavy fuel oils, and particularly to environmentally benign compositions and methods for making them burn cleanly in the form of emulsions and giving the emulsions long-term stability.
Heavy fuel oils (Numbers 4, 5 and 6) are difficult to burn cleanly. Even with properly maintained equipment of the latest design, substantial amounts of unburned carbon and other products of incomplete combustion are emitted compared to more inherently clean fuels such as gas or distillate oil. Fuels are typically atomized to enhance burning, but the droplets often burn incompletely. The result can be soot production, excessive smoke, carbon monoxide and other problems of poor combustion. One way to improve combustion is to decrease the fuel droplet size entering the flame front, allowing a smaller droplet to burn out completely during the limited time allowed for combustion.
Droplet size can be reduced by improving atomization and by introducing tiny water droplets into the oil in the form of an emulsion. These water droplets are vaporized to steam as the oil droplet starts to burn. The steam produced inside the oil droplet shatters it into many smaller droplets. A typical oil droplet is on the order of 50-100 microns in diameter and it has been found that water droplets in the range of 2-10 microns are very effective and gross water contents of 5-15% wt or so in the fuel provide enough energy to shatter most or almost all the droplets and drastically reduce particulate emissions. NOx emissions are usually reduced somewhat as well due to the fact that peak flame temperature is reduced slightly leading to a reduction in thermal NOx formation.
Emulsions have been often discussed in the literature, but there are many shortcomings in the systems useful for their production. The general process is well established and has been is use commercially on a limited scale for many years, but is in need of improvement particularly in terms of providing additional stability and environmentally compatible chemical emulsification and/or stabilization chemicals.
One problem is that chemical stabilizers are needed to keep the water in suspension and prevent the formation of free water on the bottom of the storage tank if the emulsion is meant to be stored before use or transported to a secondary location for combustion. The equipment required to make a No. 6 oil emulsion is rather expensive and these emulsions are frequently made in a single location for distribution to end user sites some distance away.
Emulsion stabilizers in commercial use today are generally surfactants designed to match the hydrophilic-lipophilic balance (HLB) requirements of No. 6 oil to reduce the surface tension at the oil-water interface and form a stable emulsion. These are both (relatively) expensive and are subject to failure when the HLB requirement of the oil changes and, because these droplets have almost no surface tension, they coalesce readily and form a water layer. Thus, when a distillate fuel is mixed with a decant fuel, usually of very different composition and HLB, the result can be similar to deliberately adding a surfactant of known wrong HLB to enhance emulsion separation such as in the case of using a de-emulsifier to break out the small amounts of water that has become emulsified in No. 6 oil during transport and handling to remove it under controlled conditions before distribution. The additive according to the invention is more stable to the variations in formulation that can be expected when using residual fuels.
The HLB requirement changes drastically when the oil characteristics change. The most prevalent comparison is between a “normal” No. 6 oil and a visbroken decant oil. The user of heavy oils often is forced to buy what is available at a low cost and make adjustments to enable efficient burning without undue creation of particulates and other pollution. It would be desirable if such a user would have emulsification additives and systems effective to permit variations in source and type of heavy oil.
Normal No. 6 oil is largely aliphatic and has a density of 1.0 and less and is very viscous. Decant oils have high aromatic contents and have densities above 1.0 and have a lower viscosity. They behave differently during emulsification and have differing stabilizing requirements. Sometimes blends of the two types of oils are commingled in commerce, and/or diluted with distillates to make a No. 5 or No. 4 oil, further complicating the picture. Number 4 and 5 fuel oils are substantially lower in viscosity, making stable emulsions even harder to maintain.
Another practical problem is encountered when a fuel distributor or the like finds water seeping into a heavy oil storage tank and needs to eliminate the tank bottom water. Typically, a distributor might burn such a fuel to maintain temperature in various heavy fuel storage tanks for ease of handling, but cannot easily burn the water contaminated fuel and cannot conveniently dispose of the water because it is contaminated. It would be desirable if there were a way to dispose of the water without pollution, ideally to use it to improve combustion by reducing particulates. The “tank water” below is difficult to emulsify due to the presence of unknown and widely varying contaminants.
The ability to effectively emulsify the water in the tank into the fuel would solve the disposal problem and it would help in reducing particulate emissions; however, this can be accomplished only where the emulsion is stable over a wide range of HLB values due to the variation in such for heavy oils. Also, to assure proper emulsion formation, the tank water must be removed from the tank and sometimes there is a need to supplement the tank water. Thus, the system is highly complex, yet the emulsification must be reproducible and stand up to wide variations in HLB and water mineral contents.
There is a need for a system and additives for emulsification of added and/or tank water to serve two purposes: (1) the elimination of a source of polluted water that must be otherwise disposed of, and (2) the reduction of particulate emissions normally visible when burning normal No. 6 oil.